Vibration element, vibrator, oscillator, electronic apparatus, and moving object

ABSTRACT

A vibration element includes a piezoelectric substrate including a vibrating section and a thick section having a thickness larger than that of the vibrating section. The thick section includes a first thick section provided along a first outer edge of the vibrating section, a second thick section provided along a second outer edge, and a third thick section provided along another first outer edge. An inclined outer edge section that intersects with each of an X axis and a Z′ axis is provided in a tip section of the piezoelectric substrate.

BACKGROUND

1. Technical Field

The present invention relates to a vibration element, a vibrator, anoscillator, an electronic apparatus and a moving object.

2. Related Art

An AT-cut quartz crystal vibration element shows a thickness shearvibration in a vibration mode of a main vibration for excitation. Sincethe AT-cut quartz crystal vibration element is suitable for reduction insize and increase in frequency and provides a cubic curve having anexcellent frequency-temperature characteristic, the AT-cut quartzcrystal vibration element is used in various apparatuses such as apiezoelectric oscillator and an electronic apparatus.

JP-A-2002-198772 discloses an AT-cut quartz crystal vibration elementhaving an inverted mesa structure that includes a thin vibrating sectionand a thick section provided around the entire periphery of thevibrating section. The AT-cut quartz crystal vibration element is fixedto a package through an adhesive agent in one end portion of the thicksection. In a state where the AT-cut quartz crystal vibration element iscantilevered, if an acceleration in a thickness direction is applied tothe AT-cut quartz crystal vibration element, a tip section (thevibrating section) is deformed, which causes a problem in that avibration characteristic (frequency characteristic) is not stable. Inparticular, in the AT-cut quartz crystal vibration element disclosed inJP-A-2002-198772, since the thick section is formed over the entireperiphery of the vibrating section and the weight of the tip section isheavy, the influence on the acceleration is large, and accordingly, theamount of frequency deviation is also increased.

SUMMARY

An advantage of some aspects of the invention is to provide a vibrationelement, a vibrator, an oscillator, an electronic apparatus and a movingobject capable of reducing change in a vibration characteristic due toan external force such as an acceleration (vibration) while suppressingincrease in size (increase in thickness) to achieve a stable vibrationcharacteristic.

The invention can be implemented as the following application examples.

Application Example 1

This application example is directed to a vibration element including: asubstrate that includes a first region having a vibration region thatvibrates with a thickness shear vibration, and a second region that isintegrated with the first region and has a thickness larger than that ofthe first region; and excitation electrodes that are respectivelyprovided on front and rear surfaces of the vibration region. The firstregion includes first outer edges that are provided on one side and theother side in a vibration direction of the thickness shear vibration,and second outer edges that are provided on one side and the other sidein a direction that intersects with the vibration direction, the secondregion includes a first thick section that is provided along the firstouter edge on the one side and is provided with a fixing section to befixed to a target, and a second thick section that is provided along thesecond outer edge on the one side and is connected to the first thicksection. The second outer edge on the other side is exposed in across-sectional view of the substrate, and an inclined outer edgesection that is inclined with respect to both of the vibration directionand the direction that intersects with the vibration direction isprovided at a corner of the first outer edge side on the other side andthe second outer edge side on the other side in the substrate, in a planview of the substrate.

With this configuration, it is possible to obtain a vibration element inwhich the mass on the tip side (opposite to the fixing section) isreduced, change in a vibration characteristic due to an external forcesuch as acceleration (vibration) is suppressed and a stable vibrationcharacteristic is achieved. Further, it is possible to reduce thethickness of the thick section, and to suppress increase in the size ofthe vibration element.

Application Example 2

In the vibration element according to the application example, it ispreferable that, when the length of the substrate in the vibrationdirection is L and the length of the first region in the vibrationdirection is L1, the relationship of L1/L≦0.52 is satisfied.

With this configuration, it is possible to reduce deformation of thefirst region due to an external force such as acceleration (vibration).

Application Example 3

In the vibration element according to the application example, it ispreferable that, in the plan view of the substrate, when the length ofthe substrate in a direction orthogonal to the vibration direction is Wand the length of the first region in the direction orthogonal to thevibration direction is W1, the relationship of W1/W≧0.5 is satisfied.

Thus, it is possible to reduce deformation of the first region due to anexternal force such as acceleration (vibration).

Application Example 4

In the vibration element according to the application example, it ispreferable that an inclination angle of the inclined outer edge sectionwith respect to the vibration direction is 40° or greater and 50° orsmaller.

With this configuration, it is possible to effectively achieve the massreducing effect of the inclined outer edge section.

Application Example 5

In the vibration element according to the application example, it ispreferable that, when a maximum thickness of the second region is Tmaxand a minimum thickness thereof is Tmin, an average thickness of(Tmax+Tmin)/2 is 50 μm or greater and 70 μm or smaller.

With this configuration, it is possible to form the first region withhigh accuracy while increasing rigidity of the vibration element.

Application Example 6

In the vibration element according to the application example, it ispreferable that the first outer edge on the other side is exposed.

With this configuration, it is possible to reduce the mass on the tipside of the vibration element.

Application Example 7

In the vibration element according to the application example, it ispreferable that the second region includes a third thick section that isprovided along the first outer edge on the other side and is connectedto the second thick section.

With this configuration, it is possible to increase the rigidity of thefirst region, and to reduce deformation of the first region due to anexternal force such as acceleration (vibration).

Application Example 8

In the vibration element according to the application example, it ispreferable that when an electrical axis, a mechanical axis and anoptical axis that are crystal axes of a quartz crystal are respectivelyrepresented as an X axis, a Y axis and a Z axis, and when an axisobtained by inclining the Z axis so that a +Z side is rotated in a −Ydirection of the Y axis is represented as a Z′ axis and an axis obtainedby inclining the Y axis so that a +Y side is rotated in a +Z directionof the Z axis is represented as a Y′ axis, using the X axis as arotation axis, the substrate is a quartz crystal plate in which asurface including the X axis and the Z′ axis corresponds to a mainsurface and a direction of the Y′ axis corresponds to a thickness.

With this configuration, it is possible to obtain a vibration elementhaving an excellent temperature characteristic.

Application Example 9

This application example is directed to a vibrator including thevibration element described above and a package in which the vibrationelement is accommodated.

With this configuration, it is possible to obtain a vibrator with highreliability.

Application Example 10

This application example is directed to an oscillator including thevibration element described above and an oscillation circuit that drivesthe vibration element.

With this configuration, it is possible to obtain an oscillator withhigh reliability.

Application Example 11

This application example is directed to an electronic apparatusincluding the vibration element described above.

With this configuration, it is possible to obtain an electronicapparatus with high reliability.

Application Example 12

This application example is directed to a moving object including thevibration element described above.

With this configuration, it is possible to obtain a moving object withhigh reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a perspective view illustrating a vibration element accordingto a first embodiment of the invention.

FIG. 2 is a plan view illustrating the vibration element shown in FIG.1.

FIG. 3 is a diagram illustrating the relationship between an AT-cutquartz crystal substrate and a crystal axis of a quartz crystal.

FIG. 4 is a side view illustrating a state where the vibration elementshown in FIG. 1 is fixed to a target.

FIG. 5 is a graph illustrating the relationship between the size of aninclined edge part and G sensitivity.

FIG. 6 is a graph illustrating the relationship between the thickness ofa thick section and G sensitivity.

FIG. 7 is a graph illustrating the relationship between the width of athird thick section and G sensitivity.

FIG. 8 is a graph illustrating the relationship between the width of thethird thick section and the amount of deformation.

FIGS. 9A to 9E are diagrams illustrating patterns for reducing the massof a tip section of the vibration element.

FIG. 10 is a graph illustrating the relationship between the moment of aremoved section of each pattern shown in FIGS. 9A to 9E and Gsensitivity.

FIG. 11 is a graph illustrating the relationship between a crystal axisof a quartz crystal and stress sensitivity.

FIG. 12 is a plan view illustrating a vibration element according to asecond embodiment of the invention.

FIG. 13 is a perspective view illustrating a vibration element accordingto a third embodiment of the invention.

FIG. 14 is a cross-sectional view illustrating an embodiment suitablefor a vibrator according to the invention.

FIG. 15 is a cross-sectional view illustrating an embodiment suitablefor an oscillator according to the invention.

FIG. 16 is a perspective view illustrating a configuration of a mobile(or note-type) personal computer to which an electronic apparatusaccording to the invention is applied.

FIG. 17 is a perspective view illustrating a configuration of a mobilephone (including a PHS) to which an electronic apparatus according tothe invention is applied.

FIG. 18 is a perspective view illustrating a configuration of a digitalstill camera to which an electronic apparatus according to the inventionis applied.

FIG. 19 is a perspective view schematically illustrating an automobilethat is an example of a moving object according to the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, a vibration element, a vibrator, an oscillator, anelectronic apparatus and a moving object according to the invention willbe described in detail with reference to preferable embodiments shown inthe accompanying drawings.

1. Vibration Element

First, the vibration element according to the invention will bedescribed.

First Embodiment

FIG. 1 is a perspective view illustrating a vibration element accordingto a first embodiment of the invention. FIG. 2 is a plan viewillustrating the vibration element shown in FIG. 1. FIG. 3 is a diagramillustrating the relationship between an AT-cut quartz crystal substrateand a crystal axis of a quartz crystal. FIG. 4 is a side viewillustrating a state where the vibration element shown in FIG. 1 isfixed to a target. FIG. 5 is a graph illustrating the relationshipbetween the size of an inclined edge section and G sensitivity. FIG. 6is a graph illustrating the relationship between the thickness of athick section and G sensitivity. FIG. 7 is a graph illustrating therelationship between the width of a third thick section and Gsensitivity. FIG. 8 is a graph illustrating the relationship between thewidth of the third thick section and the amount of deformation. FIGS. 9Ato 9E are diagrams illustrating patterns for reducing the mass of a tipsection of the vibration element. FIG. 10 is a graph illustrating therelationship between the moment of a removed section of each patternshown in FIGS. 9A to 9E and G sensitivity. FIG. 11 is a graphillustrating the relationship between a crystal axis of a quartz crystaland stress sensitivity. Hereinafter, for ease of description, a rightside in FIG. 2 is referred to as a tip, and a left side therein isreferred to as a base end.

As shown in FIGS. 1 and 2, a vibration element 1 includes apiezoelectric substrate (substrate) 2, and an electrode 3 formed on thepiezoelectric substrate 2.

Piezoelectric Substrate

The piezoelectric substrate 2 is a plate-like quartz crystal substrate.Here, a quartz crystal that is a material of the piezoelectric substrate2 belongs to a trigonal system, and has crystal axes X, Y and Z that areorthogonal to each other, as shown in FIG. 3. The X axis, Y axis and Zaxis are referred to as an electrical axis, a mechanical axis, and anoptical axis, respectively. The piezoelectric substrate 2 of the presentembodiment is a “rotated Y-cut quartz crystal substrate” cut along aplane obtained by rotating an XZ plane around the X axis by apredetermined angle θ, in which a substrate cut along a plane obtainedby a rotation of θ=35° 15′, for example, is referred to as an “AT-cutquartz crystal substrate”. By using such a quartz crystal substrate, thevibration element 1 having an excellent temperature characteristic isachieved. Here, as the piezoelectric substrate 2, instead of the AT-cutpiezoelectric substrate, any substrate that can excite a thickness shearvibration, for example, a BT-cut piezoelectric substrate may be used.

Hereinafter, the Y axis and the Z axis rotated around the X axiscorresponding to the angle θ are set as a Y′ axis and a Z′ axis. Thatis, the piezoelectric substrate 2 has a thickness in the Y′ axisdirection, and has an area in an XZ′ plane direction.

The piezoelectric substrate 2 forms an approximately rectangular shapein which a direction along the X axis corresponds to long sides and adirection along the Z′ axis corresponds to short sides in a plan view.Further, in the piezoelectric substrate 2, the −X axis directioncorresponds to the tip side, and the +X axis direction corresponds tothe base end side.

As shown in FIGS. 1 and 2, the piezoelectric substrate 2 includes avibrating section (a first region) 21 having a thin vibration region (aregion where vibration energy is confined) 219, and a thick section (asecond region) 22 that is integrated with the vibrating section 21 andhas a thickness larger than that of the vibration region 219. Thevibrating section 21 may be formed by forming a recessed section by wetetching on a main surface of the quartz crystal substrate on a +Y axisside, for example.

The vibrating section 21 is shifted in the −X axis direction and the −Z′axis direction with reference to the center of the piezoelectricsubstrate 2, of which a part of an outer edge is exposed from the thicksection 22. Specifically, the vibrating section 21 includes a pair offirst outer edges 211 and 212 that are separated in the X axis direction(a movement direction of the thickness shear vibration) and extend inthe Z′ axis direction (a direction intersecting with the X axisdirection) in the plan view of the vibration element 1; and a pair ofsecond outer edges 213 and 214 that are separated in the Z′ axisdirection and extend in the x axis direction. Among the first outeredges 211 and 212, the first outer edge 211 is positioned on the +X axisside, and the first outer edge 212 is positioned on the −X axis side.Further, among the second outer edges 213 and 214, the second outer edge213 is positioned on the +Z′ axis side, and the second outer edge 214 ispositioned on the −Z′ axis side.

The thick section 22 is provided to surround three sides of thevibrating section 21. As shown in FIG. 1, a front surface (main surfaceon the +Y′ axis direction side) of the thick section 22 is provided toprotrude toward the +Y′ axis direction side from a front surface (mainsurface on the +Y′ axis direction side) of the vibrating section 21. Onthe other hand, a rear surface (main surface on the −Y′ axis directionside) of the thick section 22 is provided on the same plane as a rearsurface (main surface on the −Y′ axis direction side) of the vibratingsection 21.

As shown in FIGS. 1 and 2, the thick section 22 includes a first thicksection 23 disposed along the first outer edge 211, a second thicksection 24 disposed along the second outer edge 213, and a third thicksection 25 that is disposed along the first outer edge 212 and isconnected to the second thick section 24. Accordingly, the thick section22 forms a structure curved along the vibrating section 21 in the planview. On the other hand, the thick section 22 is not formed at thesecond outer edge 214 of the vibrating section 21, and the second outeredge 214 is exposed from the thick section 22. In this way, by partiallyproviding the thick section 22 along the outer edge of the vibratingsection 21 except for the second outer edge 214, it is possible toreduce the mass of the vibration element 1 on the tip side whilesecuring rigidity of the vibration element 1 (vibrating section 21).Further, it is possible to achieve reduction in the size of thevibration element 1.

Here, by providing the second thick section 24 on the +Z′ axis side withrespect to the vibrating section 21, it is possible to shorten the width(length in the Z′ axis direction) of an inclined section 241 (to bedescribed later), compared with a case where the second thick section 24is provided on the −Z′ axis side. Thus, according to the thick section22 having such a configuration, it is possible to achieve reduction inthe size of the vibration element 1.

The first thick section 23 includes an inclined section (residualsection) 231 that is connected to the first outer edge 211 and has athickness gradually increasing in the +X axis direction, and a thicksection main body 232 that is connected to an end edge of the inclinedsection 231 on the +X axis direction side and has an approximatelyuniform thickness. Similarly, the third thick section 25 includes aninclined section (residual section) 251 that is connected to the firstouter edge 212 and has a thickness gradually increasing in the −X axisdirection, and a thick section main body 252 that is connected to an endedge of the inclined section 251 on the −X axis direction side and hasan approximately uniform thickness. Similarly, the second thick section24 includes the inclined section (residual section) 241 that isconnected to the second outer edge 213 and has a thickness graduallyincreasing in the +Z′ axis direction, and a thick section main body 242that is connected to an end edge of the inclined section 241 on the +Z′axis direction side and has an approximately uniform thickness.

On the front surface of the thick section main body 232 of the firstthick section 23, that is, on the base end side of the vibration element1, a mounting section (fixing section) 29 is provided. As shown in FIG.4, the vibration element 1 is fixed to a target 92 using an adhesivematerial 91 through the mounting section 29. The position of themounting section 29 is not particularly limited, and for example, themounting section 29 may be provided on the rear surface of the thicksection main body 232.

Electrode

The electrode 3 includes a pair of excitation electrodes 31 and 32, apair of pad electrodes 33 and 34, and a pair of extraction electrodes 35and 36. The excitation electrode 31 is formed on the front surface ofthe vibration region 219. On the other hand, the excitation electrode 32is formed to be opposite to the excitation electrode 31 on the rearsurface of the vibration region 219. The excitation electrodes 31 and 32form an approximately rectangular shape in which the X axis directioncorresponds to long sides and the Z′ axis direction corresponds to shortsides, respectively. Further, the area of the excitation electrode 32 onthe rear side is larger than that of the excitation electrode 31 on thefront surface side, and the entire region of the excitation electrode 31is positioned within the excitation electrode 32 in the plan view of thevibration element 1.

The pad electrode 33 is formed in the mounting section 29 of the frontsurface of the thick section main body 232. On the other hand, the padelectrode 34 is formed to be opposite to the pad electrode 33 on therear surface of the thick section main body 232.

The extraction electrode 35 extends from the excitation electrode 31,and the excitation electrode 31 and the pad electrode 33 areelectrically connected to each other through the extraction electrode35. Further, the extraction electrode 36 extends from the excitationelectrode 32, and the excitation electrode 32 and the pad electrode 34are electrically connected to each other through the extractionelectrode 36. The extraction electrode 36 is provided to not overlap theextraction electrode 35 through the piezoelectric substrate 2 in theplan view. Thus, it is possible to suppress an electrostatic capacitancebetween the extraction electrodes 35 and 36.

A configuration of the electrode 3 is not particularly limited, but forexample, a metal coating obtained by layering Au (gold), Al (aluminum)or an alloy containing Au (gold) or Al (aluminum) as a main component ona base layer made of Cr (chrome), Ni (nickel) or the like may be used.

Hereinbefore, a basic configuration of the vibration element 1 isdescribed. Next, the appearance of the vibration element 1 will bedescribed in detail. The size of each section in the followingdescription becomes a particularly effective value when the appearance(length L and width W) of the vibration element 1 is in a predeterminedrange. The predetermined range is a range that satisfies therelationship of L≦5 mm and the relationship of W≦3 mm.

As shown in FIGS. 1 and 2, an inclined outer edge section 26 that isinclined with respect to each of the X axis direction and the Z′ axisdirection is provided in a corner section of the piezoelectric substrate2 positioned on the side of the first outer edge 212 and the side of thesecond outer edge 214, in the plan view. The inclined outer edge section26 is provided so that the corner section positioned on the −X axis sideand the −Z′ axis side is cut. By providing the inclined outer edgesection 26, it is possible to reduce the mass of the vibration element 1on the tip side. Thus, as shown in FIG. 4, in a state where thevibration element 1 is fixed to the target through the adhesive materialin the mounting section 29, it is possible to reduce the amount ofdeformation of the vibration element 1 on the tip side (vibratingsection 21) when an acceleration in the Y′ axis direction is applied tothe vibration element 1. As a result, it is possible to reduce change ina vibration characteristic (frequency) due to an acceleration in the Y′axis direction, and to abate sensitivity of the vibration element 1 tothe acceleration in the Y′ axis direction. Accordingly, the vibrationelement 1 can achieve a stable vibration characteristic regardless ofwhether the acceleration in the Y′ axis direction is applied. Further,according to the vibration element 1, since it is possible tosufficiently abate the sensitivity of the vibration element 1 to theacceleration in the Y′ axis direction, for example, it is not necessaryto excessively increase the thickness of the thick section 22 toincrease the rigidity, thereby preventing increase in the size of thevibration element 1.

Here, an inclination angle θ1 of the inclined outer edge section 26 withrespect to the X axis is not particularly limited, but is preferably 40°or more and 50° or less, and more preferably about 45°. In the presentembodiment, the angle is about 45°. Thus, it is possible to effectivelyachieve the mass reducing effect. Further, it is preferable that theinclined outer edge section 26 be provided over a part of the vibratingsection 21. Thus, it is possible to increase the size of the inclinedouter edge section 26, to thereby noticeably achieve the above-mentionedeffect.

Change in a G sensitivity characteristic due to change in the size ofthe inclined outer edge section 26 when an acceleration is applied inthe Y′ axis direction is shown in a graph of FIG. 5. In FIG. 5, a lengthL26 shown in FIG. 2 is represented as the size of the inclined outeredge section 26. As shown in FIG. 5, it can be understood that thefrequency change decreases and the sensitivity to the acceleration inthe Y′ axis direction is abated as the size of the inclined outer edgesection 26 increases. FIG. 5 is a graph illustrating the tendency of thevibration element 1 as an example, and thus, the vibration element 1 isnot limited to numerical values shown in FIG. 5.

Further, when the width (length in the Z′ axis direction) of thepiezoelectric substrate 2 is W and the width (length in the Z′ axisdirection) of the vibrating section 21 is W1, it is preferable that thevibration element 1 satisfy the relationship of W1/W≧0.5. Thus, it ispossible to decrease a width W24 of the second thick section 24, and toreduce the mass of the vibration element 1 on the tip side. Thus, it ispossible to provide the vibration element 1 capable of abating thesensitivity of the vibration element 1 to the acceleration in the Y′axis direction and of achieving a stable vibration characteristicregardless of whether the acceleration in the Y′ axis direction isapplied.

Here, if the width W24 is excessively decreased, it is difficult tosufficiently secure the rigidity of the vibrating section 21 dependingon the value of the width W1, and thus, the deformation of the vibratingsection 21 may be increased. In other words, the effect obtained byreducing the mass on the tip side may be less than a bad influencecaused by decrease in the rigidity. Thus, it is preferable to satisfythe relationship of W1/W≦0.8. That is, by satisfying the relationship of0.5≦W1/W≦0.8, it is possible to effectively abate the sensitivity of thevibration element 1 to the acceleration in the Y′ axis direction.Accordingly, the vibration element 1 can achieve a stable vibrationcharacteristic regardless of whether the acceleration in the Y′ axisdirection is applied.

Further, when the length of the piezoelectric substrate 2 (length in theX axis direction) is L and the length of the vibrating section 21(length in the X axis direction) is L1, it is preferable that thevibration element 1 satisfy the relationship of L1/L≦0.52. Thus, theoccupancy rate of the first thick section 23 in the piezoelectricsubstrate 2 is sufficiently increased, and thus, it is possible tosufficiently increase the rigidity of the vibration element 1. Thus, thevibrating section 21 is not easily deformed, and thus, it is possible toabate the sensitivity of the vibrating element 1 to the acceleration inthe Y′ axis direction. Accordingly, the vibration element 1 can achievea stable vibration characteristic regardless of whether the accelerationin the Y′ axis direction is applied. The first thick section 23 ispositioned on the base end side with reference to the vibrating section21. Thus, the first thick section 23 serves as a section thatcontributes to increasing the rigidity of the vibrating section 21, anddoes not serve as a weight that deforms the vibrating section 21.Accordingly, by increasing the size of the first thick section 23, it ispossible to sufficiently abate the sensitivity of the vibration element1 to the acceleration in the Y′ axis direction. Since a lower limitvalue of L1/L varies according to the sizes of the excitation electrodes31 and 32, the lower limit value is not particularly limited.

A thickness T of the piezoelectric substrate 2 (an average thickness of(Tmax+Tmin)/2 when a maximum thickness is Tmax and a minimum thicknessis Tmin) is not particularly limited, but it is preferable to satisfythe relationship of 50 μm≦T≦70 μm. Thus, it is possible to form thevibrating section 21 with high accuracy while securing the rigidity ofthe vibration element 1. Thus, the vibration element 1 can stablyachieve a desired vibration characteristic. On the other hand, if thethickness T is less than the lower limit value, the rigidity of thevibration element 1 may become insufficient according to the mass (thelength L, the width W and the like) of the vibration element 1, andthus, it may be difficult to sufficiently reduce the amount ofdeformation of the tip section (vibrating section 21) of the vibrationelement 1 when the acceleration in the Y′ axis direction is applied tothe vibration element 1. In contrast, if the thickness T exceeds theupper limit value, the size of the vibration element 1 may excessivelybecome large, or the yield of the vibration element 1 may be reduced.Specifically, as described above, the vibrating section 21 is obtainedby forming the recessed section on the main surface on the +Y′ side bywet etching. Here, if the thickness T increases, the recessed sectionbecomes deep. Accordingly, the widths of the inclined sections 231, 241and 251 increase. Thus, the size of the vibration element 1 increases.Further, if the thickness T increases, the depth (etching depth) of therecessed section becomes deep, which degrades the etching accuracy.Thus, it is difficult to adjust the vibrating section 21 to a desiredthickness, and thus, the yield of the vibration element is reduced.

The change in the G sensitivity characteristic due to the change in thethickness T when the acceleration in the Y′ axis direction is applied isshown in a graph of FIG. 6. As shown in FIG. 6, it can be understoodthat the frequency change decreases and the sensitivity to theacceleration in the Y′ axis direction is abated as the thickness Tincreases. FIG. 6 shows results about four samples. Further, FIG. 6 is agraph illustrating the tendency of the vibration element 1 as anexample, and thus, the vibration element 1 is not limited to numericalvalues shown in FIG. 6.

Further, it is preferable that a width (an average size of a maximumsize and a minimum size of the thick section main body 252) W25 of thethird thick section 25 be equal to or smaller than 100 μm. Thus, it ispossible to sufficiently reduce the mass of the third thick section 25,and to reduce the mass of the vibration element 1 on the tip side. Thus,it is possible to suppress the change in the vibration characteristicdue to the acceleration in the Y′ axis direction, and to provide thevibration element 1 capable of achieving a stable vibrationcharacteristic regardless of whether the acceleration in the Y′ axisdirection is applied.

Change in the G sensitivity characteristic due to change in the widthW25 when an acceleration is applied in the Y′ axis direction is shown ina graph of FIG. 7. As shown in FIG. 7, it can be understood that thefrequency change decreases and the sensitivity to the acceleration inthe Y′ axis direction is abated as the width W25 decreases. Change inthe amount of deformation when acceleration loads of two vibrationelements having different widths W25 are applied in the −Y′ axisdirection is shown in FIG. 8. In FIG. 8, the width W25 of the vibrationelement indicated by a solid line is set to be smaller than the widthW25 of the vibration element indicated by a dashed line, and thevibration element indicated by the solid line has a small amount ofdeformation. Thus, it can be understood that the sensitivity of thevibration element 1 having the small width W25 to the acceleration inthe Y′ axis direction is abated. FIGS. 7 and 8 are graphs respectivelyillustrating the tendency of the vibration element 1 as an example, andthus, the vibration element 1 is not limited to the numerical valuesshown in FIGS. 7 and 8.

Here, from the viewpoint of the mass reducing effect of the tip sectionof the vibration element 1, the small width W25 is preferable. However,if the width W25 is excessively small, the strength of the vibrationelement 1 is excessively reduced depending on the thickness T of thethick section 22, which may cause damage of the vibration element 1.Thus, from the viewpoint of securing a mechanical strength of thevibration element 1, it is preferable that the width W25 be 40 μm orgreater. That is, by satisfying the relationship of 40 μm≦W25≦100 μm, itis possible to reduce the mass of the tip section of the vibrationelement 1 while securing the mechanical strength of the vibrationelement 1. Thus, it is possible to decrease the amount of deformation ofthe vibration element 1 on the tip side when the acceleration in the Y′axis direction is applied to the vibration element 1, and thus, thevibration element 1 can achieve a stable vibration characteristicregardless of whether the acceleration in the Y′ axis direction isapplied. Further, by satisfying the relationship of 45 μm≦W25≦55 μm, itis possible to remarkably achieve the above-described effect.

As described above, according to the vibration element 1 of the presentembodiment, the mass on the tip side is reduced, and the change in thevibration characteristic due to the acceleration applied in the Y′ axisdirection is reduced, thereby making it possible to achieve a stablevibration characteristic.

Here, in order to reduce the mass of the tip section of the vibrationelement shown in FIG. 9A, as shown in FIG. 9B, the width of the thicksection main body 252 may be reduced, as shown in FIG. 9C, the width ofthe thick section main body 242 may be reduced, as shown in FIG. 9D, acorner of the tip section on the +Z′ axis side may be removed, or asshown in FIG. 9E, a corner of the tip section on the −Z′ axis side maybe removed. Hereinafter, a pattern shown in FIG. 9B is referred to as apattern P1, a pattern shown in FIG. 9C is referred to as a pattern P2, apattern shown in FIG. 9D is referred to as a pattern P3, and a patternshown in FIG. 9E is referred to as a pattern P4.

Influences of the respective patterns P1 to P4 on the G sensitivitycharacteristic are shown in FIG. 10. The horizontal axis in the graph ofFIG. 10 represents a value of [mass of a removed section (sectionsurrounded by a dashed line)]x[separation distance between the center ofgravity of the removed section and a fulcrum point (mounting section29)], which is referred to as a “moment” hereinafter. The vertical axisin the graph of FIG. 10 represents a standardized G sensitivity, whichis a value obtained by standardizing a G sensitivity of each of thepatterns P1 to P4 when the G sensitivity of the vibration element shownin FIG. 9A is set to “1”.

It can be understood from FIG. 10 that changes in the G sensitivitycharacteristics are different in the patterns P1 to P4. For example, theG sensitivity decreases as the removed section is enlarged in thepatterns P1, P3 and P4, whereas the G sensitivity increases as theremoved section is enlarged in the pattern P2. Further, in the patternsP1, P3 and P4, the G sensitivity linearly decreases in proportional tothe size of the removed section without being saturated in the patternsP1 and P3, whereas the decrease of the G sensitivity is almost saturatedif the size of the removed section is a predetermined value or greaterin the pattern P4. It is considered that the difference between the Gsensitivity characteristic changes of the patterns P1 to P4 is causeddue to the crystal axes of the quartz crystal and the shape of thevibration element.

FIG. 11 is a graph illustrating the relationship of a resonancefrequency due to a force F applied to a quartz crystal vibrator anddisplacement. When an intersection angle between the force F and the Xaxis of the quartz crystal is ψ, if ψ=0°, the force F acts along the Xaxis direction, and if ψ=90°, the force F acts along the Z′ axisdirection.

Further, it can be understood from FIG. 11 that a stress sensitivity(Kf) is reversed in positivity and negativity between the X axis and theZ′ axis. It is considered that this reversion is a factor that causesthe difference between the pattern P1 and the pattern P2. Further, sinceit is considered that each of the patterns P3 and P4 is a combination ofthe patterns p1 and P2, it is considered that the patterns P3 and P4show different characteristics from those of the patterns P1 and P2.Further, it is considered that the difference between the patterns P3and P4 is also caused due to the difference between the shapes of thevibration element 1, in addition to the stress sensitivity. That is, inthe pattern P3, since the thick section 22 occupies the entirety of theremoved section regardless of the size of the removed section, the Gsensitivity is linearly abated according to the size of the removedsection. On the other hand, in the pattern P4, the ratio of thevibrating section 21 occupied by the removed section increases as theremoved section is enlarged, the mass reducing effect is reduced, andthe decrease of the G sensitivity is saturated.

In this way, the present inventors found that it is possible to select amethod of changing the G sensitivity according to how to reduce the massof the tip section of the vibration element. In the vibration element 1,by selecting the pattern P4 from among the patterns P1 to P4, it ispossible to reduce the mass of the tip section and to improve the Gsensitivity characteristic. It can be understood from FIG. 10 that thepattern P4 has the highest initial G sensitivity reducing effect amongthe patterns P1 to P4. Thus, by selecting the pattern P4, it is possibleto effectively abate the sensitivity of the vibration element 1 to theacceleration in the Y′ axis direction. Accordingly, the vibrationelement 1 can achieve a stable vibration characteristic regardless ofwhether the acceleration in the Y′ axis direction is applied. Asdescribed above, in the pattern P4, the saturation point of the Gsensitivity reducing effect is present. Thus, it is preferable that theinclined outer edge section 26 be designed so that the moment is closeto the saturation point. Accordingly, it is possible to maximize theeffect of the pattern P4, and to prevent excessive increase in the sizeof the inclined outer edge section 26.

Second Embodiment

Next, a second embodiment of a vibration element of the invention willbe described.

FIG. 12 is a plan view of the vibration element according to the secondembodiment of the invention.

Hereinafter, differences between the vibration element of the secondembodiment and the vibration element of the first embodiment will bemainly described, and description about the same content will not berepeated.

The vibration element according to the second embodiment of theinvention is the same as that of the first embodiment, except for theconfiguration of the piezoelectric substrate. The same components as inthe first embodiment are given the same reference numerals.

As shown in FIG. 12, in the vibration element 1 of the presentembodiment, the third thick section 25 is not provided, and the firstouter edge 212 and the second outer edge 214 are exposed from the thicksection 22, respectively. In this way, as the thick section 22 ispartially provided along the outer edge of the vibrating section 21 toform an approximate L shape and is not provided along the first outeredge 212 and the second outer edge 214, it is possible to reduce themass of the vibration element 1 on the tip side while securing therigidity of the vibration element 1 (vibrating section 21). Further, itis possible to achieve reduction in the size of the vibration element 1.Particularly, it is possible to reduce the mass of the vibration element1 on the tip side, compared with the first embodiment.

According to the second embodiment, it is possible to achieve the sameeffect as in the first embodiment.

Third Embodiment

Next, a third embodiment of the vibration element of the invention willbe described.

FIG. 13 is a perspective view illustrating the vibration elementaccording to the third embodiment of the invention.

Hereinafter, differences between the vibration element of the thirdembodiment and the vibration element of the first embodiment will bemainly described, and description about the same content will not berepeated.

The vibration element according to the third embodiment of the inventionis the same as that of the first embodiment, except for theconfiguration of the piezoelectric substrate. The same components as inthe first embodiment are given the same reference numerals.

As shown in FIG. 13, in the vibration element 1 of the presentembodiment, by forming recessed sections on the both main surfaces ofthe piezoelectric substrate 2, the vibrating section 21 is formed. Inother words, the front surface (main surface on the +Y′ axis directionside) of the thick section 22 is provided to protrude in the +Y′ axisdirection with reference to the front surface (main surface on the +Y′axis direction side) of the vibrating section 21, and the rear surface(main surface on the −Y′ axis direction side) of the thick section 22 isprovided to protrude in the −Y′ axis direction with respect to the rearsurface (main surface on the −Y′ axis direction side) of the vibratingsection 21. In this way, by forming the recessed sections on the bothmain surfaces of the piezoelectric substrate 2 to form the vibratingsection 21, for example, it is possible to reduce the etching depth ofthe recessed sections, compared with the above-described firstembodiment. Thus, it is possible to perform the etching with accuracy,and to obtain the outer shape of the piezoelectric substrate 2 with highaccuracy.

According to the third embodiment, it is possible to achieve the sameeffect as in the first embodiment.

2. Vibrator

Next, a vibrator (vibrator according to the invention) to which theabove-described vibration element 1 is applied will be described.

FIG. 14 is a cross-sectional view illustrating an embodiment suitablefor the vibrator of the invention.

A vibrator 10 shown in FIG. 14 includes the above-described vibrationelement 1, and a package 4 that accommodates the vibration element 1.

Package

The package 4 includes a base 41 of a box shape having a recessedsection 411 with an opening at an upper surface thereof, and a lid 42 ofa plate shape bonded to the base 41 to block the opening of the recessedsection 411. Further, the vibration element 1 is accommodated in anaccommodating space S formed as the recessed section 411 is blocked bythe lid 42. The accommodating space S may be in a decompression (vacuum)state, or may be sealed with an inert gas such as nitrogen, helium orargon.

A component material of the base 41 is not particularly limited, butvarious ceramics such as aluminum oxide may be used. Further, acomponent material of the lid 42 is not particularly limited, but amember having a linear expansion coefficient close to that of thecomponent material of the base 41 may be used. For example, when thecomponent material of the base 41 is the above-described ceramics, analloy such as Kovar may be preferably used. The bonding of the base 41and the lid 42 is not particularly limited, but for example, may beperformed using an adhesive material, or may be performed using seamwelding or the like.

On the bottom surface of the recessed section 411 of the base 41,connection electrodes 451 and 461 are formed. Further, on the lowersurface of the base 41, outer mounting terminals 452 and 462 are formed.The connection electrode 451 is electrically connected to the outermounting terminal 452 through a through electrode (not shown) formed inthe base 41, and the connection electrode 461 is electrically connectedto the outer mounting terminal 462 through a through electrode (notshown) formed in the base 41. Configurations of the connectionelectrodes 451 and 461 and the outer mounting terminals 452 and 462 arenot particularly limited as long as they have conductivity,respectively. For example, the connection electrodes 451 and 461 and theouter mounting terminals 452 and 462 may be formed by a metal coatingobtained by layering a coating made of Ni (nickel), Au (gold), Ag(silver), Cu (copper) or the like on a metalized layer (base layer) madeof Cr (chrome), W (tungsten) or the like.

The vibration element 1 accommodated in the accommodating space S isfixed to the base 41 by a conductive adhesive material 51 in themounting section 29 with the front surface thereof being directed towardthe base 41 side. The conductive adhesive material 51 is provided incontact with the connection electrode 451 and the pad electrode 33.Thus, the connection electrode 451 and the pad electrode 33 areelectrically connected to each other through the conductive adhesivematerial 51. By supporting the vibration element 1 at one place (onepoint) using the conductive adhesive material 51, for example, it ispossible to suppress stress generated by the vibration element 1 due tothe difference between the thermal expansion coefficients of the base 41and the piezoelectric substrate 2.

The conductive adhesive material 51 is not particularly limited as longas it has conductivity and adhesiveness, but for example, a materialobtained by dispersing a conductive filler into an adhesive material ofa silicone base, an epoxy base, an acrylic base, a polyimide base, abismaleimide base or the like may be used.

The pad electrode 34 of the vibration element 1 is electricallyconnected to the connection electrode 461 through a bonding wire 52. Asdescribed above, since the pad electrode 34 is disposed to face the padelectrode 33, in a state where the vibration element 1 is fixed to thebase 41, the pad electrode 34 is disposed directly above the conductiveadhesive material 51. Thus, it is possible to suppress leakage ofvibration (ultrasonic vibration) given to the pad electrode 34 in wirebonding, and to reliably perform the connection of the bonding wire 52to the pad electrode 34.

3. Oscillator

Next, an oscillator (oscillator according to the invention) to which thevibration element according to the invention is applied will bedescribed.

FIG. 15 is a cross-sectional view illustrating an embodiment suitablefor the oscillator of the invention.

An oscillator 100 shown in FIG. 15 includes the vibrator 10, and an ICchip 110 for driving the vibration element 1. Hereinafter, differencesbetween the oscillator 100 and the above-described vibrator will bemainly described, and description about the same content will not berepeated.

As shown in FIG. 15, in the oscillator 100, the IC chip 110 is fixed tothe recessed section 411 of the base 41. The IC chip 110 is electricallyconnected to plural internal terminals 120 formed on the bottom surfaceof the recessed section 411. A part of the plural internal terminals 120are connected to the connection electrodes 451 and 461, and theremaining part thereof are connected to the outer mounting terminals 452and 462. The IC chip 110 has an oscillation circuit for performing adrive control of the vibration element 1. If the vibration element 1 isdriven by the IC chip 110, it is possible to extract a signal of apredetermined frequency.

4. Electronic Apparatus

Next, an electronic apparatus (electronic apparatus according to theinvention) to which the vibration element according to the invention isapplied will be described.

FIG. 16 is a perspective view illustrating a configuration of a mobile(or note-type) personal computer to which the electronic apparatusaccording to the invention is applied. In FIG. 16, a personal computer1100 includes a main body section 1104 provided with a keyboard 1102,and a display unit 1106 provided with a display section 2000. Thedisplay unit 1106 is supported to the main body section 1104 to berotatable through a hinge structure. The vibrator 10 (vibration element1) that functions as a filter, a resonator, a reference clock or thelike is built in the personal computer 1100.

FIG. 17 is a perspective view illustrating a configuration of a mobilephone (including a PHS) to which the electronic apparatus according tothe invention is applied. In FIG. 17, a mobile phone 1200 includesplural operation buttons 1202, an ear piece 1204 and a mouthpiece 1206,and a display section 2000 is disposed between the operation buttons1202 and the ear piece 1204. The vibrator 10 (vibration element 1) thatfunctions as a filter, a resonator or the like is built in the mobilephone 1200.

FIG. 18 is a perspective view illustrating a configuration of a digitalstill camera to which the electronic apparatus according to theinvention is applied. In FIG. 18, connection to an external device isalso simply shown. Here, an ordinary camera has a configuration in whicha silver salt photo film is exposed to a light image of an object,whereas a digital still camera 1300 has a configuration in which a lightimage of an object is photoelectrically converted by an imaging elementsuch as a charged coupled device (CCD) to generate an imaging signal(image signal).

A display section is provided on a rear surface of a case (body) 1302 inthe digital still camera 1300 to perform display based on the imagingsignal obtained by the CCD. The display section functions as a finderthat displays the object as an electronic image. Further, a lightreceiving unit 1304 that includes an optical lens (imaging opticalsystem), a CCD or the like is provided on a front surface side (rearsurface side in the figure) of the case 1302.

If a user checks an object image displayed in the display section andpresses a shutter button 1306, an imaging signal of the CCD at that timeis transmitted to and stored in a memory 1308. Further, in the digitalstill camera 1300, a video signal output terminal 1312, and a datacommunication input/output terminal 1314 are provided on a side surfaceof the case 1302. Further, as shown in the figure, a television monitor1430 is connected to the video signal output terminal 1312, and apersonal computer 1440 is connected to the data communicationinput/output terminal 1314, as necessary. Further, the imaging signalstored in the memory 1308 is output to the television monitor 1430 orthe personal computer 1440 by a predetermined operation. The vibrator 10(vibration element 1) that functions as a filter, a resonator or thelike is built in the digital still camera 1300.

The electronic apparatus provided with the vibration element accordingto the invention may be applied to an ink jet discharge device (forexample, an ink jet printer), a laptop personal computer, a television,a video camera, a video tape recorder, a car navigation device, a pager,an electronic organizer (including the one having a communicationfunction), an electronic dictionary, a calculator, an electronic gamemachine, a word processor, a work station, a television phone, a crimeprevention TV monitor, electronic binoculars, a POS terminal, a medicaldevice (for example, an electronic thermometer, a blood manometer, ablood sugar level meter, an electrocardiographic measuring device, anultrasonic diagnostic device or an electronic endoscope), a fish-finder,a variety of measuring devices, a meter (for example, a meter for avehicle, an airplane or a ship), a flight simulator or the like, forexample, in addition to the personal computer (mobile personal computer)shown in FIG. 16, the mobile phone shown in FIG. 17 and the digitalstill camera shown in FIG. 18.

5. Moving Object

Next, a moving object (moving object according to the invention) towhich the vibration element according to the invention is applied willbe described.

FIG. 19 is a perspective view schematically illustrating an automobilethat is an example of the moving object according to the invention. Thevibrator 10 (vibration element 1) is mounted on an automobile 1500. Thevibrator 10 may be widely applied to an electronic control unit (ECU)such as a keyless entry, an immobilizer, a car navigation system, a carair-conditioner, an anti-lock braking system (ABS), an air bag, a tirepressure monitoring system (TPMS), an engine controller, a batterymonitor of a hybrid automobile or an electric car, or a vehicle attitudecontrol system.

Hereinbefore, the vibration element, the vibrator, the oscillator, theelectronic apparatus and the moving object according to the inventionhave been described with reference to the embodiments shown in thedrawings, but the invention is not limited thereto. The configurationsof the respective sections may be replaced with arbitrary configurationshaving the same functions. Further, other arbitrary configurations maybe added to the invention. Further, the above-described embodiments maybe appropriately combined.

Further, in the above-described embodiments, the quartz crystalsubstrate is used as the piezoelectric substrate, but for example,various piezoelectric substrates made of lithium niobate, lithiumtantalite or the like may be used instead of the quartz crystalsubstrate.

The entire disclosure of Japanese Patent Application No. 2013-075014,filed Mar. 29, 2013 is expressly incorporated by reference herein.

What is claimed is:
 1. A vibration element comprising: a substrate thatincludes a first region having a vibration region that vibrates with athickness shear vibration, and a second region that is integrated withthe first region and has a thickness larger than that of the firstregion; and excitation electrodes that are respectively provided onfront and rear surfaces of the vibration region, wherein the firstregion includes first outer edges that are provided on one side and theother side in a vibration direction of the thickness shear vibration,and second outer edges that are provided on one side and the other sidein a direction that intersects with the vibration direction, wherein thesecond region includes a first thick section that is provided along thefirst outer edge on the one side and is provided with a fixing sectionto be fixed to a target, and a second thick section that is providedalong the second outer edge on the one side and is connected to thefirst thick section, wherein the second outer edge on the other side isexposed in a cross-sectional view of the substrate, and wherein aninclined outer edge section that is inclined with respect to both of thevibration direction and the direction that intersects with the vibrationdirection is provided at a corner of the first outer edge side on theother side and the second outer edge side on the other side in thesubstrate, in a plan view of the substrate.
 2. The vibration elementaccording to claim 1, wherein when the length of the substrate in thevibration direction is L and the length of the first region in thevibration direction is L1, the relationship of L1/L≦0.52 is satisfied.3. The vibration element according to claim 1, wherein, in the plan viewof the substrate, when the length of the substrate in a directionorthogonal to the vibration direction is W and the length of the firstregion in the direction orthogonal to the vibration direction is W1, therelationship of W1/W≧0.5 is satisfied.
 4. The vibration elementaccording to claim 2, wherein, in the plan view of the substrate, whenthe length of the substrate in a direction orthogonal to the vibrationdirection is W, and the length of the first region in the directionorthogonal to the vibration direction is W1, the relationship ofW1/W≧0.5 is satisfied.
 5. The vibration element according to claim 1,wherein an inclination angle of the inclined outer edge section withrespect to the vibration direction is 40° or greater and 50° or smaller.6. The vibration element according to claim 2, wherein an inclinationangle of the inclined outer edge section with respect to the vibrationdirection is 40° or greater and 50° or smaller.
 7. The vibration elementaccording to claim 3, wherein an inclination angle of the inclined outeredge section with respect to the vibration direction is 40° or greaterand 50° or smaller.
 8. The vibration element according to claim 4,wherein an inclination angle of the inclined outer edge section withrespect to the vibration direction is 40° or greater and 50° or smaller.9. The vibration element according to claim 1, wherein when a maximumthickness of the second region is Tmax and a minimum thickness thereofis Tmin, an average thickness of (Tmax+Tmin)/2 is 50 μm or greater and70 μm or smaller.
 10. The vibration element according to claim 2,wherein when a maximum thickness of the second region is Tmax and aminimum thickness thereof is Tmin, an average thickness of (Tmax+Tmin)/2is 50 μm or greater and 70 μm or smaller.
 11. The vibration elementaccording to claim 3, wherein when a maximum thickness of the secondregion is Tmax and a minimum thickness thereof is Tmin, an averagethickness of (Tmax+Tmin)/2 is 50 μm or greater and 70 μm or smaller. 12.The vibration element according to claim 4, wherein when a maximumthickness of the second region is Tmax and a minimum thickness thereofis Tmin, an average thickness of (Tmax+Tmin)/2 is 50 μm or greater and70 μm or smaller.
 13. The vibration element according to claim 8,wherein when a maximum thickness of the second region is Tmax and aminimum thickness thereof is Tmin, an average thickness of (Tmax+Tmin)/2is 50 μm or greater and 70 μm or smaller.
 14. The vibration elementaccording to claim 1, wherein the first outer edge on the other side isexposed.
 15. The vibration element according to claim 1, wherein thesecond region includes a third thick section that is provided along thefirst outer edge on the other side and is connected to the second thicksection.
 16. The vibration element according to claim 1, wherein when anelectrical axis, a mechanical axis and an optical axis that are crystalaxis of a quartz crystal are respectively represented as an X axis, a Yaxis and a Z axis, and when an axis obtained by inclining the Z axis sothat a +Z side is rotated in a −Y direction of the Y axis is representedas a Z′ axis and an axis obtained by inclining the Y axis so that a +Yside is rotated in a +Z direction of the Z axis is represented as a Y′axis, using the X axis as a rotation axis, the substrate is a quartzcrystal plate in which a surface including the X axis and the Z′ axiscorresponds to a main surface and a direction of the Y′ axis correspondsto a thickness.
 17. A vibrator comprising: the vibration elementaccording to claim 1; and a package in which the vibration element isaccommodated.
 18. An oscillator comprising: the vibration elementaccording to claim 1; and an oscillation circuit that drives thevibration element.
 19. An electronic apparatus comprising the vibrationelement according to claim
 1. 20. A moving object comprising thevibration element according to claim 1.